Loaded cable



June 6, 1933. j J GILBERT 1,912,442

LOADED CAB'LE Filed Oct. 30, 1930 2 Sheets-Sheet 1 %i l a M :mmg

INVENTOR J. G/L BERT 5y ATTORNEY J. J. GILBERT June 6, 1933.

LOADED CABLE 2 Sheets-Sheet 2 Filed Oct. 30 1930 SELECTED PO/NTJ 0NCABLE FIG. 4

lNl/ENTOR J. J. GIL BER B) ATTORNEY layer through This invention relatesto signaling conductors and more particularly to continuously loadedconductors for the transmission of telephone and telegraph currents.naling circuit.

This invention is applicable to the usual type of continuously loadedconductors in which the loading is effected by wrapping a wire or tapeof magnetic material around a central conductor. The tape forms a thinich runs a helical air-gap. The lines of magnetic induction set up in eribed follow a helical path through the loading material. Owing to thepresence of the air-gap, the magnetic flux due to currents in thecentral conductor may be resolved into two components, one parallel thesame cable. to the length of the tape and the other parallel to theplane of the tape but perpendicu- The latter component is longitudinalwith respect to the axis of the conductor and will hereinafter bereferred to as the longitudinal component of maglt should be noted thatthis theory is not in agreement with the comconductors. monly acceptedand widespread idea that the lines of magnetic induction around the larto its length.

discussion of the magnetic inloaded cable of this character, referenceis made to Patent 1,586,962 issued June 1, 1926 to O. E. Buckley.

nal component of magnetic induction of a loaded conductor creates anumber of undesirable results, among them n to impair the efiiciency ofthe conduceffects are eliminated. tor I01 signaling purposes. The usualsub- A further object of this invention is to marine cable, in additionto surrounding ayer of insulation, is further surrounded by onc uctingmaterial composed of the sea rmor wire. This conducting maforms a pathfor eddy currents which 4 up by the longitudinal flux in the resistancein the conducting mate- Patente-d June 65, 1933 LOADED CABLE Applicationfiled October 30, 1930. Serial No. 492,134.

STATES PATENT OFFICE JOHN J. GILBERT, 01 DGUGLASTON, NEW YORK, ASSIGNORT0 BELL TELEPHONE LAB- OnATCR-IES, INCORPORATED, OF NEW YORK, N. Y., ACORPORATION OF NEW YORK rial and thus energy is dissipated. The effectof the wasted energy manlfests itself 111 an increase mthe attenuationof the sig- A longitudinal component of magnetic 5 flux may beobjectionable in the case of a multi-conductor telegraph or telephonecable in which each pair of conductors forms an individual circuit, aswell as in the case of a cable in which the pairs are grouped to 5 formquads for the well known phantom cirtne loading material by a conductorof the cuit arrangement. The longitudinal components of flux resultingfrom two conductors in the same circuit, unless neutralized, by eachother, produce a resultant flux which may cause cross-talk in adjacentcircuits in An object of this invention is to reduce cross-talk due tolongitudinal magnetic induction in a multi'conductor cable.

Another object of this invention is to reduce eddy current losses due tolongitudinal magnetic induction in a cable in which there is one or morecircuits formed by pairs of 7 The above objects are obtained by pairingthe conductors so that the longitudinal coinconductor form closed loops.For a more ponent of induction of one conductor balances orneutralizesthat of the other. If the loading tapes on the two conductors have 7exactly the same permeability, thickness, width and lay, and thecurrents are equal and opposite, the longitudinal induction componentsof the two conductors are balanced and the cross-talk and eddy currentally manufac- The eddy currents enlaying operation. Owing to inherentmanufacturing conditions the electrical properof several feet.

ties of the individual sections will not be identical. In accordancewith this invention, the longitudinal flux component of each section fora given current is separately measured and sections having nearlyidentical longitudinal flux components are paired or twinned.

It has been hitherto proposed to eliminate the longitudinal inductioncomponent of a loaded conductor by cons ructing the cable exactly inaccordance with an accurate design. See Patent 1,674,912, issued June26, 1926 to U. Meyer. lls contrasted with this method, the presentinvention obviates the necessity of painstalringjcare in the manufactureof the cables. The difference between the permeability of the loadingmaterial of one cable section and that of another section is compensatedin the process of matching the cable sections after they have beenmanufactured and tested.

Fig. 1 of the accompanying drawings show a twin core submarine cableconstructed in accordance with this invention;

Fig. 2 shows an arrangement for testing the loaded conductors beforethey are matched with each other;

Fig. 3 is a curve plotted from readings taken by the ballisticgalvanometer shown in Fig. 2;

Fig. 4 shows a number of loaded conductors arranged to form a multipletwin quad; and

Fig. 5 shows a device similar to that of Fig. 2 for testing a pair ofconductors intended for use in forming a multiple twin quad. 7

Referring to the submarine cable shown in Fig. l, the central copperconductors 9 are surrounded by a number of segments 11, say six, shapedto fit the central conductors 10. Upon the segments 11 is applied ahelix of loading material 12. Suitable loading materials and suitablemethods of applying loading materials are known and need not bediscussed herein. The conductor is heat treated after the loadingmaterial is applied thereto. Suitable heat treating methods such as arewell known may be employed. The loading material is surrounded by apressure equalizing fluid, su h as liquid bitumen or depolymerizedrubber. Surrounding the loading material is a sheath of insulatingmaterial 13 such as gutta percha or gutta percha substitute. The entirestructure thus far described constitutes a unit hereinafter referred toas a core. Two such cores are twinned together in a twinning machine andgiven a spiral lay or pitch. The pitch is preferably of the order Thecores 13 are surrounded by the usual jute, teredo tape and armor wire,not shown.

In the process of manufacture of the cores,

"the loading tapes on the two conductors are constructed to have, asnearly as possible, the same permeability, thickness, width and lay. Twocores are arranged to form a twowire circuit, with the loading tapes ofthe two cores having the same direction of lay as illustrated in Fig. 1.Assuming that the two cores are matched perfectly, the longitudinalcomponent of magnetic induction set up by one conductor will beneutralized by the corresponding component set up by the otherconductor.

In practice, the dimensions, permeability and lay of the loading tapevary slightly, and to compensate for corresponding variations in themagnetic field, a number of sections of loaded conductors of about amile in length, and approximately similar in construct-ion, areseparately measured and from the measurements taken, two conductorsections are selected which when paired together will most nearlyneutralize each others longitudinal flux component.

Fig. 2 shows an arrangement for recording the longitudinal component ofmagnetic induction at dill'erent points along the length of a loadedconductor. The conductor 10 after being wrapped with loading material iswound upon a paying-out reel 20 and is adapted to pass from that reel toanother reel 21. The cable is connected electrically with the reels andwith the supports 22 for the same. The supports 22 are insulated fromeach other by insulating blocks 23, and are connected to form a seriescircuit with the conductor 10, a battery 24, a key 25, an ammeter 2G anda rheostat 27. A solenoid or exploring coil 30 surrounds the conductor10 and is supported by suitable means, not shown. A two-poledouble-throw switch 32 is connected to the terminals of the solenoid 30,and is adapted, when thrown in one position, to connect the solenoid toa ballistic galvanometer 35. In its other position the switch 32connects the terminals of the solenoid through an amplifier 37,preferably of the thermionic vacuum tube type, to a flux meter 40.

Upon opening and closing the key 25 an electromot-ive force will beinduced in the solenoid having a value which depends upon thelongitudinal flux component of the conductor 10. A reading is taken onthe ballistic galvanometer at the instant that the key is closed oropened. The conductor 10 is then moved to a different position relativeto the solenoid 30, and another reading taken on the ballisticgalvanomctcr. A series of readings thus taken may be plotted, as shownin Fig. 3. The ordinates of the curve in Fig. 8 represent the values oflongitudinal fiuX component at di ferent points along the conductor 10.A. similar set of readings is taken for another cable section,

and another curve similar to Fig. 3 is plotted. The curves for thedifferent cable sections are compared, and those sections whose curvesapproximately coincide are paired with each other. In taking thesemeasurements it is necessary that the steady direct current through theconductor 10 following each closing or preceding each opening of the key25 be keptat approximately the same value. This current can be regulatedconveniently by the rhcostat 2?.

A more expeditious method of obtaining flux readings for the purposes ofcomparison may be employed by using the flux meter 40 in conjunctionwith the ballistic galvanometer 35.

The flux meter l0 should be of the type which integrates changes inmagnetic field over a long period of time before the indicating elementof the flux meter creeps apprcciably toward the zero position. The fluxmeter readings are taken while the conductor 10 is moved, at anapproximately uniform rate, through the solenoid 30. During the time thereadings are taken, a steady dir ct current flows through the conductor.The initial reading of the flux meter may be taken by closing the key 25after the conductor 10 has started moving. The flux meter indicatingelement moves from its zero position to a position representing thelongitudinal flux component at one point on the conductor 10. As thelongitudinal flux within the solenoid 30 increases or decreases, thedeflection of the indicating element increases or decreasescorrespondingly.

The readings of the flux meter may be ob served at regular intervalswhile the conductor 10 is moving and may be plotted to obtain a curvesimilar to the one shown in Fig. 3. A more convenient method, however,is to provide the flux meter with an arrangement for recording thedeflections automatically.

The satisfactory operation of the flux meter method of measuringlongitudinal flux as described above, is dependent to a large extentupon the property of the indi eating element to remain in the sameposition when the longitudinal flux is distributed evenly along theconductor 10, and there is hence no electromotive force induced in thesolenoid 30. If the indicating element of the flux meter, under theseconditions creeps toward the zero position, errors in the readings willcumulate. As a check upon the flux meter readings the switch 32 may bethrown occasionally to the opposite position and one or more readingsmay be taken with theballistic galvanometer 35.

While two methods have been described for measuring and recording thelongitudinal flux component of a conduct )r, it is to be understood thatthere are othe" methods, whereby these same readings may be recorded.For example, the arrangement shown in the patent issued to O. E. BuckleyNo. 1,586,962, June 1, 1926 is suitable for the purpose mentioned.

F 4 shows a multi-conductor cable comprising two conductors 51 and 52twisted upon each other to form one pair, and two other conductors 53and 54, respectively, which are similarly twisted to form a second pair.Each pair of conductors forms a two wire circuit. The two pairs ofconductors are twisted upon each other to form a quad. Each conductor isseparately loaded by a helical tape and insulated preferably by paper.Each conductor, being loaded, sets up a magnetic field which has acomponent longitudinal with respect to the conductor. If the twoconductors of a pair are properly matched in accordance with the methoddescribed above, the rcsultant longitudinal component of magneticinduction will be zero. However, if no attempt has been made to matchthe conductors of each pair, or if the conductors have been matchedimperfectly, an arrangement may be employed for neutralizing theresultant longitudinal flux component of one pair of conductors with theresultant component from. another pair of conductors, of which the twopairs form a quad.

An arrangement for measuring the resultant longitudinal flux componentof a pair of conductors 51 and 52 is shown in Fig. 5. A device similarto that shown in Fig. 2 is provided, but in the device of Fig. 7.

5 it is necessary to provide a slip ring arrangement so that the ends ofthe conductors 51 and 52 may be connected to the battery 6st. Theconductors 51 and 52 are connected to each other electrically at one endwhereby the two conductors carry the same current in oppositedirections. The slip rings 65 and 66, respectively, are connected to thefree ends of the conductors 51 and 52 and cooperate with brushes 67 and68 to? connect the conductors 51 and 52 serially with the battery Gl-"and an arrangement which consists of a key, ammeter and rheostatsimilar to those shown in Fig. 2. The

solenoid may be connected in the same manner as the solenoid 30 of Fig.2.

As an alternative to the arrangement of Fig. 5 the resultantlongitudinal flux component at any point along a pair of loadedconductors may be computed by plotting" one pair with that of anotherpair of con-' ductors, crosstalk between the two pairs may be avoided.

What is claimed is:

1. A continuously loaded multi-conductor cable for communicationpurposes, compris-i ing two adjacent conductors each surrounded withhelically arranged loading material and matched by having the loadingmaterials arranged with the same permeability, thickness, width, and layin corresponding portions so that in each section the longitudinalcomponent of magnetic induction due to one conductor is balanced by thelongitudinal component due to the other conductor.

2. A signalling cable, each section of which comprises a group ofconductors matched so that the longitudinal component of magneticinduction due to one conductor is balanced by the longitudinal componentdue to another conductor.

3. A continuously loaded communication cable of twin core typecharacterized in this, that two core lengths selected from a number ofsections and constituting a twin core section are more nearly equal toeach other in respect to their inductance in a longitudinal directionthan they are equal to the cores of other sections of the number fromwhich the sections were selected, said core lengths being arranged sothat said inductance components are, opposite in direction.

4. The method of constructing a continuously loaded communication cablewhich comprises selecting from a number of core lengths, pairs of corelengths having as nearly as possible equality of inductionlongitudinally of the cores to form a twin core section, and arrangingthe cores so that their longitudinal inductance components are oppositein direction.

5. In a multi-conductor cable, the method of neutralizing the componentof magnetic induction longitudinally of the cable, which methodcomprises selecting a number of conductor lengths, subjecting eachlength to the same current condition, measuring the longitudinalinduction component at correspending points on the respective conductorlengths and pairing conductor lengths having nearly equal measurements.

6. A method of determining two conductors most nearly matched as totheir longitudinal component of magnetic induction, which methodcomprises measuring the longitudinal induction component at acorresponding point on each one of a number of such conductors when theconductors are subjected to similar current conditions, and comparingthe measurements thus taken.

7. A method of constructing a two conductor cable with conductors mostnearly matched as to their longitudinal component of magnetic induction,which method comprises measuring the longitudinal induction component ata plurality of correspond ing points on each one of a number of lengthsof conductors, comparing curves plotted with the measurements thustaken,

and pairing lengths of conductors whose curves approximately coincide.

8. A multi-conductor communication cable comprising a plurality of pairsof continuously loaded conductors, said conductors being so selectedthat the resultant longitudinal component of magnetic inductionv due toone pair of conductors is opposite and approximately equal to thelongitudinal induction component resulting from a second pair ofconductors by which the first pair is closely paralleled.

9. In a communication cable comprising a number of pairs of continuouslyloaded conductors, the method of neutralizing the component of magneticinduction longitudinally of the cable, which method comprises selectinga number of pairs of conductors subjecting each pair to the same currentcondition, measuring the resultant longitudinal induction component ofeach pair, at corresponding points on the several pairs, and groupingtwo pairs having nearly equal measurements to form a quad.

In Witness whereof, I hereunto subscribe my name this 20 day of October,1930.

JOHN J. GILBERT.

